Dwarfed even by the freight cars it is switching, the diminutive No. 100 works the Galesburg yard during 1929, shortly after its purchase. Inefficient in this service, the Mack was soon relegated to the Galesburg tie plant, where it put in over 20 years of uneventful service. Hol also included the following detailed history of the Mack:

When the Q sought to buy its first internal combustion locomotive for switching service in 1928, it turned to none other than Mack again ( having earlier purchased gas-electric motorcar 501 in 1922 ), because EMC had nothing to offer in the switcher field. What the railroad got was a tiny 30-ton, rigid frame, four-wheel, center-cab gas-electric locomotive just over 16' long. Powered by a pair of four-cylinder. 85-hp Mack truck engines, the diminutive switcher utilized General Electric electrical equipment - generators and traction motors. Cooling radiators were mounted atop the cab roof instead of the more common "winter-front" position at the ends of the hoods. Built by Mack at its Plainfield, NJ plant in November 1928 ( c/n 172001 ), the locomotive was the first model AW turned out ( only three others followed ), and was used as a demonstrator. The Q acquired it on March 20, 1929, after testing it extensively in yard and industrial switching service at Lincoln, NE. Numbered 100, the little 170-hp center-cab machine was painted solid Pullman green with gold numbers and CB&Q initials. Immediately the 100 was assigned to Galesburg, where it worked industrial trackage and the railroad's tie plant. Designed to exert 18,000 pounds of tractive force at 30% adhesion below one mile per hour, 7,000 pounds at five miles an hour, and 4,000 pounds at 10 mph, the 100 supposedly could haul 650 tons at nine miles per hour on level track or 200 tons on a 1% grade at a lower speed. This made the locomotive inefficient in all but the lightest switching chores, so by the early 1930's the 100 was assigned strictly to the Galesburg tie plant ( and equipped with large buffer plates ). Beginning in 1932, 9000-series numbers were assigned to Q gas-electric ( and soon diesel-electric ) switching power, but the tiny 100, confined to the tie plant, was not renumbered to 9100 until October 1939. And it kept the number for just one year, because the operation department decided to differentiate tie plant switchers with their own numbers so that some unknowing dispatcher wouldn't inadvertently try to assign the little machines to regular switching duties. And so, in October 1940, the Mack AW assumed its third and final number: 8900. It continued its uneventful and little photographed life in the Galesburg tie plant until finally, in August 1952, the nearly 24-year-old locomotive was retired and scrapped.